Characterization of CdS and ZnS thin films deposited by RF sputtering method and usage in the fabrication heterojunctions

The CdS and ZnS II–VI compounds are of great importance in the optoelectronic applications, for example, in solar cells, optical sensors, infrared windows because of its direct and wide band gap at room temperature. This study presents the effects of substrate temperature on morphological and optical properties of radio frequency (RF) sputtered CdS and ZnS thin films. The thin films were formed on p–Si wafer and soda lime glasses at 40, 150 and 275 oC using high purity CdS and ZnS targets. Morphological properties of CdS and ZnS thin films were analyzed by the help of atomic force microscopy (AFM) and scanning electron microscopy (SEM) methods. The optical properties of sputtered the thin films were determined using UV–vis data. It was seen that substrate temperature had strong effects on physical characteristics of thin films. Ag/CdS/p–Si and Ag/ZnS/p–Si heterojunction diodes were fabricated by thermally evaporation. Electrical and photoelectrical properties of the heterojunctions were analyzed at room temperature by means of current–voltage (I–V) measurements of devices in dark and under a solar simulator with various illumination intensities. The heterojunctions were showed good rectifying behavior by the I–V curves at room temperature. The barrier height, ideality factor and series resistance parameters were investigated using its current–voltage (I–V) measurements. Obtained results have been compared with available results of CdS and ZnS heterjunction contacts in literature. Key Words: CdS, ZnS, SEM, AFM, heterojunction, barrier height, ideality factor and series resistance.